YozoraAtlas

How dark is the sky in Southwest Finland?

Sky darkness for 6 towns and parks in Southwest Finland, worked out from NASA satellite images of light at night (2025). 1 of them has skies of Bortle 4 or darker, where the Milky Way shows overhead. The darkest is Kurjenrahka National Park (20.66, Bortle 4), the brightest Turku (17.69, Bortle 8). The bright core of the Milky Way never climbs clear of the horizon haze anywhere in Southwest Finland while the sky is fully dark; the rest of the band passes overhead, with the longest moonless nights from October to March.

19 Bortle class, 1 pristine to 9 city center park or dark-sky place city

Numbers like 21.95 or 16.97 are the brightness of the sky overhead on a clear, moonless night, in mag/arcsec². The scale runs backwards: a lower number means a brighter sky, from about 22 for a natural sky to about 17 in a city center.
How the readings are made

NASA satellite night-lights map of Southwest Finland with every place marked

Darkest skies in Southwest Finland

  1. Kurjenrahka National ParkBortle 420.66

Among the places on this site. Plenty of land between them is just as dark, with no town or park to name it by.

Brightest city skies in Southwest Finland

  1. TurkuBortle 817.69
  2. SaloBortle 718.89
  3. NaantaliBortle 718.94
  4. LietoBortle 619.27

All 6 places in Southwest Finland

Amber names are parks and certified dark-sky places. The figure is the Bortle class: 1 darkest, 9 city center.
Kurjenrahka National Park4Lieto6Naantali7Salo7Teijo National Park6Turku8